Fuel injection system for internal combustion engines

ABSTRACT

A fuel injection system for internal combustion engines having a plurality of fuel injectors, in which the fuel injectors each have one high-pressure connection and one low-pressure connection, and the low-pressure connections discharge into at least one manifold line. The system has a means, located between the manifold line and a pressureless fuel return, for maintaining the fuel pressure; at least one throttle is located between the low-pressure connection of each fuel injector and the means for maintaining the fuel pressure.

FIELD OF THE INVENTION

In storage-type injection, or “common rail injection”, pressuregeneration and injection are decoupled from one another. The injectionpressure is generated independently of the engine rpm and of theinjection quantity and is available in the “rail”—that is, the fuelreservoir—for injection. The instant of injection and the injectionquantity are calculated in the electronic control unit and are convertedby an injector at each engine cylinder. The injector has the task ofadjusting the injection onset and the injection quantity.

Besides triggering the injector via a piezoelectric element, triggeringthe injector via a magnet valve is also known. While in magnet valvessufficiently long valve strokes can be generated for using the magnetvalve as a control valve, in control of an injector with a piezoelectricelement additional provisions must be made. The reason is that with apiezoelectric element, only a very short stroke, which is in the rangeof only some thousandths of the length of the piezoelectric element, canbe generated. For the actuation of the adjusting valve, this shortstroke must be transformed during continuous operation of the injector.For this purpose, a hydraulic booster is for instance used.

PRIOR ART

In the prior art, control and leakage quantities from the injector orinjectors are carried away via a pressureless fuel return and fed intothe fuel tank. In some injectors for diesel engines, the leak fuel inthe injector must have a defined pressure, however. These injectorsinclude piezoelectrically controlled common rail injectors. In theseinjectors, a hydraulic coupler is located between the piezoelectricactuator and the control valve and lengthens the adjustment path of thepiezoelectric actuator. To that end, there is a coupling chamber, whosefilling requires a defined leak fuel pressure that is above the ambientpressure.

From German Patent Disclosure DE-A 199 52 513, a fuel injection systemfor internal combustion engines is known, having at least one injectorwhich communicates with a pressureless fuel return. Between the injectoror injectors and the fuel return, there are means for maintaining a leakfuel pressure in the injector or injectors. In particular, the means formaintaining a leak fuel pressure are located in the injector orinjectors of one or more pressure holding valves.

German Patent Disclosure DE-A 101 04 634 relates to a fuel injectionsystem for internal combustion engines having a plurality of injectors,in which the injectors each have one high-pressure connection and onelow-pressure connection, and the low-pressure connections discharge intoa manifold line, with a pressure holding valve located between themanifold line and a pressureless fuel return; the manifold line isembodied as a pressure reservoir.

In these fuel injection systems of the prior art, the pressure load onthe pressure holding valve for maintaining the pressure on thelow-pressure side of the injectors, at up to 20 bar, is very high. Boththe manifold line (return rail) and the actuator and a bellows that maybe present are exposed to severe stresses from this pressure as well.

SUMMARY OF THE INVENTION

The fuel injection system of the invention avoids the disadvantages thatoccur in the prior art and enables a pressure relief of a plurality ofsystem components, in particular the actuator and/or the manifold lineand/or the pressure holding valve and/or the bellows. Another advantageis that the fuel injection system of the invention can be used forcommon rail systems, in which either at least one pressure holding valveor at least one electric fuel pump puts the injector coupling chamber,for filling, under a pressure required for that. The pressure holdingvalve may optionally be omitted, providing a cost saving; the functionalscope is maintained even without pressure holding valves. Furtheradvantages of the fuel injection system of the invention are that noadditional moving internal parts are needed, thus avoiding both wear anda high production cost. In addition, no additional adjustment proceduresas in the fuel injection system of the prior art are needed.

These advantages are attained according to the invention by a fuelinjection system for internal combustion engines having a plurality offuel injectors, in which the fuel injectors each have one high-pressureconnection and one low-pressure connection, and the low-pressureconnections discharge into at least one manifold line, the system havinga means, located between the manifold line and a pressureless fuelreturn, for maintaining the fuel pressure; at least one throttle islocated between the low-pressure connection of each fuel injector andthe means for maintaining the fuel pressure.

The at least one throttle assures that the necessary pressure on thelow-pressure side of the injector at high load points will beestablished. At low load points, this is assured by the means formaintaining the fuel pressure. Since the high pressures are representedby the throttle, downstream of the throttle only the lesser pressures ofthe means for maintaining the fuel pressure are required, which thenalso brings about the substantial relief of the entire low-pressuresystem.

Besides the advantages discussed above, the fuel injection system of theinvention has the further advantage that the production cost for the atleast one throttle is very low.

In a variant of the invention, it is provided that all the injectorscommunicate with one common manifold line via their low-pressureconnections. There can then be a connecting line between the manifoldline and each individual injector, so that the manifold line can bedesigned with a short length and simple geometry. In the variant of thefuel injection system of the invention with a single manifold line forall the injectors, it suffices to provide a throttle between thelow-pressure connection of the injector and the means for maintainingthe fuel pressure, in particular in the common manifold line.

In another feature of the invention, a plurality of manifold lines areprovided. For instance, each bank of cylinders of a V engine can beassigned its own manifold line. This version of the fuel injectionsystem of the invention may have advantages in terms of the installationspace required and the expenses for connecting the low-pressureconnections of the injectors to the respective manifold line. Using aplurality of independent manifold lines requires that at least onethrottle be provided per manifold line between the low-pressureconnection of each injector and the respective means for maintaining thefuel pressure, and in particular that one throttle be disposed in eachmanifold line.

In a preferred embodiment of the present invention, the means formaintaining the fuel pressure is a pressure holding valve. Pressureholding valves are time-tested, mature components to which recourse canbe had. Preferably, in the fuel injection system of the invention with apressure holding valve, a throttle is located upstream of the inlet,toward the injectors, of the pressure holding valve. Even with thethrottle positioned upstream of the pressure holding valve, thefunctional scope of the pressure holding valve is preserved, yetcompared to the prior art, a pressure relief of the pressure holdingvalve still occurs. Moreover, the throttle produces a pressure relief offurther system components, in particular the manifold line, theactuator, and the bellows.

The bellows is embodied such that it can absorb the axial stroke of theactuator, in particular a piezoelectric actuator, for controlling theinjector. The bellows is solidly joined to the actuator and the actuatorbore, so that fluid-tight sealing of the actuator module off from theother regions of the injector is achieved.

In a further preferred embodiment of the present invention, the meansfor maintaining the fuel pressure is an electric fuel pump. In the priorart, electric fuel pumps are known, time-tested pumps, which areembodied in modular fashion and located in the tank of a motor vehicleand are used particularly for internal combustion engines in order todeliver enough fuel to them under all operating states. In the fuelinjection system with an electric fuel pump, a throttle is preferablylocated in the manifold line upstream of the electric fuel pump. In thisvariant of the present invention, the functional scope is still presenteven without a pressure holding valve, so that no pressure holding valveis required, thus reducing costs.

In a variant of the invention, the high-pressure connections of theinjectors are supplied with fuel by at least one common rail, so thatthe advantages of the fuel injection system of the invention come intoplay with so-called common rail injection systems as well.

In an augmentation of the invention, it is provided that the injectorseach include one piezoelectric element for controlling the injector andone hydraulic booster for boosting the stroke of the piezoelectricelement. By way of this embodiment of the invention, the piezoelectricelement stroke can be transmitted to an injector needle, preferably viaa hydraulic medium, in particular fuel, in a coupling chamber of thehydraulic booster; the coupling chamber can be filled with the hydraulicmedium via the at least one throttle. Because the fuel injection systemof the invention has at least one throttle between the low-pressureconnection of the injector and the means for maintaining the fuelpressure (in particular the pressure holding valve or the electric fuelpump), the pressure required for filling the coupling chamber isestablished at high load points. At low load points, this is assured bythe pressure holding valve or the electric fuel pump. Since the highcoupler filling pressures are attained by the throttle, downstream ofthe throttle only the low pressures of the pressure holding valve or theelectric fuel pump are required, which then also brings about thesubstantial relief of the entire low-pressure system. By the choice ofthe throttle diameter, the opening pressure of the pressure holdingvalve, and the pressure of the electric fuel pump, the pressure for thecoupler filling can be applied as needed.

DRAWING

The invention is described in further detail below in conjunction withthe drawing.

Shown are:

FIG. 1, a schematic illustration of a fuel injection system according tothe prior art;

FIG. 2, a fuel injection system of the invention, with an electric fuelpump;

FIG. 3, a fuel injection system of the invention, with a pressureholding valve; and

FIG. 4, a section through a fuel injector, which is subjected to fuel athigh pressure via a high-pressure collection chamber (common rail) andis triggered by an actuator embodied as a piezoelectric actuator.

VARIANT EMBODIMENTS

FIG. 1 shows a schematic illustration of a fuel injection systemaccording to the prior art.

This is a fuel injection system with six cylinders 1, which arerepresented schematically as circles. Each cylinder 1 is assigned aninjector (not shown), which has a low-pressure connection 2. Thelow-pressure connections 2 discharge into a manifold line 3. Themanifold line 3 is embodied as a pressure reservoir, in which thepressure required on the low-pressure side of the injector ismaintained. The manifold line 3 communicates, via a schematically shownpressure holding valve 4, with the pressureless fuel return 5, so thatthe same fuel pressure, which is above the ambient pressure, prevails inall the injectors. For example, the pressure holding valve does not openuntil at a pressure of 10 bar, so that the fuel pressure in the manifoldline 3 amounts to at least 10 bar.

FIG. 2 shows a fuel injection system of the invention with an electricfuel pump.

An internal combustion engine 36, shown only schematically in FIG. 2,includes six cylinders 1, which are each subjected to fuel at highpressure via a respective fuel injector 38, shown in further detail inFIG. 4. The fuel injectors shown in further detail in Fig. are disposedin the cylinder head region 37 of the engine 36. Between the manifoldline 3 and the pressureless fuel return 5, which is in communicationwith a fuel tank 35 of a vehicle, there is an electric fuel pump 6, asthe means for maintaining the fuel pressure in this variant embodimentof the invention. There is also a throttle 7 in the manifold line 3,upstream of the electric fuel pump 6. In this combination of a throttle7 and an electric fuel pump 6, no pressure holding valve is required formaintaining the fuel pressure on the low-pressure side of the injectors.Moreover, the electronic fuel pump 6 needs to pump only fuel at a lowpressure. For instance, for a cross section of the throttle 7 of 0.5 mm,a 5-bar electric fuel pump 6 suffices.

FIG. 3 shows a fuel injection system of the invention with a pressureholding valve.

The internal combustion engine 36 may for instance be designed as a6-cylinder engine, but the variant embodiment as a 6-cylinder engine isshown only as an example. Depending on the design, engines with four,five, eight or 10 or 12 cylinders may also be supplied with the fuelinjection system proposed according to the invention. In this version ofthe present invention, as the means for maintaining the fuel pressure, apressure holding valve 8 is provided between the manifold line 3 and thepressureless fuel return 5 that discharges into the fuel tank 35 of amotor vehicle. A throttle 7 is also located in the manifold line 3,upstream of the pressure holding valve 8. With this combination of thethrottle 7 and pressure holding valve 8, the pressure holding valve 8 ispressure-relieved, so that it can have a lesser opening pressure. Forinstance, for a throttle 7 with a cross section of 0.5 mm, a 5-barpressure holding valve suffices to maintain the requisite fuel pressureon the low-pressure side of the injectors.

In the illustration in FIG. 4, a fuel injector can be seen, which is incommunication with a high-pressure collection chamber (common rail) andwhich can be actuated via an actuator embodied as a piezoelectricactuator.

The fuel injector 38 shown in FIG. 4 includes a high-pressure system 9and a low-pressure system 10. The actuation of the fuel injector 38 iseffected via an actuator 11, which in the view shown in FIG. 4 isprovided with a schematically indicated piezoelectric crystal stack 12,which lengthens when electrical current is supplied to it. Thepiezoelectric crystal stack 12 acts on an adjusting piston 18. Theadjusting piston 18 acts on a hydraulic booster 13. The hydraulicbooster 13 amplifies the only short stroke of the piezoelectric crystalstack 12 when current is supplied to the actuator 11. The hydraulicbooster 13 includes an actuating piston 15, whose end face 16 protrudesinto the hydraulic coupling chamber 14 of the hydraulic booster 13. Thepiezoelectric crystal stack 12 of the actuator 11 and the couplingchamber 14 of the hydraulic booster can both be surrounded by both athin wall 43 and a bellows 42, with which the relative motion of thepiezoelectric crystal stack 12 when current is supplied to it and of theadjusting piston 18 connected to it is made possible relative to thehydraulic coupling chamber 14.

If a bellows 42 is used, on the one hand a relative motion of thepiezoelectric crystal stack 12 with respect to the hydraulic couplingchamber 14 that is integrated with the housing of the fuel injector 31and on the other sealing between the components 12 and 14 that aremovable relative to one another are attained. The hydraulic couplingchamber 14 is surrounded by a housing 44 and is subjected to thecoupling chamber pressure P_(K). From a system chamber 20, whichsurrounds both the piezoelectric crystal stack 12 and the hydraulicbooster 13, 44, the low-pressure connection 2 extends to the manifoldline 3. As shown in FIGS. 2 and 3, the respective low-pressureconnections 2 of the further cylinders 1 of the engine 36 discharge intothe manifold line 3. The manifold line 3 extends to the means formaintaining the fuel pressure, which in the variant embodimentsschematically indicated in FIGS. 2 and 3 may be embodied either as apressure holding valve 8 or by the electric fuel pump 6 for supplyingthe engine 36 with fuel or for acting on a high-pressure pump 34. Thethrottle restriction 7 is received in the manifold line 3, into whichthe various low-pressure connections 2 of the cylinders 1 coming fromthe fuel injectors 38 discharge, and the means 6, 8 for maintaining thefuel pressure in the system chamber 20. The low-pressure connection 2may for instance be embodied as a screw means, so that at the pressuresthat prevail within the system pressure chamber 20, leakage-free sealingis assured between the system chamber 20 and in the low-pressureconnection 2.

As shown in FIG. 4, the hydraulic booster 13 includes a housing 44,which defines the hydraulic coupling chamber 14. The housing 44 isbraced on one side, via a helical spring, on a support disk that isreceived on the adjusting piston 18 of the actuator 11, and on the otherside, prestressed via a further helical spring, it is braced on asupport disk which is received on the actuating piston 15. The diameterof the adjusting piston 18 is designed as larger than the diameter ofthe actuating piston 15, so that a hydraulic pressure boosting isachieved by the interpolation of the hydraulic coupling chamber 14. Theactuating piston 15 acts on a guide piston 23. The guide piston 23 is inturn guided in an outlet conduit 22, which is provided in the housing 39of the fuel injector 38. Via the outlet conduit 22, the system chamber20 and the control chamber 24 communicate with one another. The outletconduit 22, which connects the system chamber 20 and the control chamber24 to one another, is closed and opened via a closing element 19. Theclosing element 19, in the view shown in FIG. 4, is put into its closingposition, that is, its closing element seat 21, which is embodied at thepoint where the outlet conduit 22 discharges into the control chamber24. On one face end, the closing element 19, which can for instance beembodied hemispherically, is prestressed via a spring element 26. Thespring element 26, which may be a cup spring, is braced on a face end 29of an injection valve member 27 embodied in the form of a needle. Thecontrol chamber 24 is always acted upon by fuel at high pressure via ahigh-pressure line, which is connected to one of the high-pressureconnections 40 of a high-pressure collection chamber 31 (common rail).The high-pressure collection chamber 31 is subjected to fuel at highpressure in turn via a supply line 32 via a high-pressure pump 34 andstores this fuel at high pressure. The high-pressure pump 34may—depending on the configuration of the injection system of the engine36—be preceded by an electric fuel pump 6 acting as a prefeed pump.

The system chamber 20 of the fuel injector 38, on its low-pressure side10, may be defined on one side by a thin-walled wall 43; on the otherside, the system chamber 20 may also be sealed off by a bellows 42. Theembodiment of a boundary of the system chamber 20 via a deformablebellows 42 in particular advantageously affords the possibility ofcompensating for elongations that occur because of an increase in lengthof the piezoelectric crystal stack 12 when current is supplied to theactuator, while simultaneously maintaining the sealing action. Via thepressure prevailing in the system chamber 20, filling of the hydrauliccoupling chamber 14 is effected. Between the housing 44, which surroundsthe hydraulic coupling chamber 14, and the actuating piston 15 and theadjusting piston 18, gaps are formed by way of which the fuel volume onthe low-pressure side 10 of the fuel injector 38 also enters thehydraulic coupling chamber 14 for initially filling it.

First, the situation in which the fuel injection system shown in Fig.for direct-injection internal combustion engines includes a pressureholding valve 8 on the low-pressure side 10 of the fuel injector 38 willbe considered.

If in a fuel injection system configured in this way fordirect-injection internal combustion engines 36, the control chamber 24is pressure-relieved by way of current being supplied to the actuator11, fuel flows out of the control chamber 24 into the system chamber 20via the outlet conduit 22. From the system chamber 20, the fuel volumediverted from the control chamber 24 flows via the connection 17 intothe low-pressure connection 2. All the low-pressure connections 2 of thefuel injectors 38 discharge into the manifold line 3. The further fuelinjectors 38 of the engine 36 are shown only schematically in FIG. 4. Inthe manifold line 3, the throttle 7 is received upstream of the inlet41, toward injectors, of the pressure holding valve 8. By means of thethrottle restriction 7 in the manifold line 3, it can advantageously beassured that the pressure required for filling the hydraulic couplingchamber 14 will be established at high load points. At low load points,conversely, the pressure level required for filling the hydrauliccoupling chamber 14 can be brought to bear via the pressure holdingvalve 8. At low load points, the pressure level on the low-pressure side10 of the fuel injector 38 in the system chamber 20 is dimensioned suchthat filling of the hydraulic coupling chamber 14 can be effected viathe gaps between the housing 44 and the adjusting piston 18, on the onehand, and via the gap between the actuating piston 15 and the housing 44of the pressure booster 13. At low load points, downstream of thethrottle 7 only the low pressures that can be generated by the pressureholding valve now prevail, as a result of which the substantial reliefof the low-pressure side 10 of the fuel injector 38 is achieved. Withthe dimensioning of the diameter of the throttle restriction 7 or of theopening pressure of the pressure holding valve 8—in this configurationof a fuel injection system—it is possible if needed to adjust thepressure required for filling the hydraulic coupling chamber 14 via thesystem chamber 20.

In the variant embodiment described above of a fuel injection system forinternal combustion engines, the feeding of fuel from the fuel tank 35to the high-pressure pump 34, in which compression of the fuel to a veryhigh pressure of approximately 1500 bar and more takes place, iseffected via a first fuel supply line 8.1.

If in a variant of a fuel injection system, an electric fuel pump 6,which in this case represents the means for holding the pressure, isprovided, then upon a pressure relief of the control chamber 24 byprovision of current supply to the actuator 11, an outflow of fuelvolume from the control chamber 24 into the system chamber 20 takesplace, analogously to the variant embodiment described above of a fuelsystem with a pressure holding valve 8. From the system chamber 20, thefuel flows via the connection 17 into the low-pressure connection 2,which applies to all the fuel injectors 38, which are provided for theengine in a number matching the number of cylinders of the engine 36 tobe supplied with fuel. In this case, in the manifold line 3, into whichall the low-pressure connections 2 of the fuel injectors 38 discharge, athrottle restriction 7 is again embodied. The throttle restriction 7 islocated at the discharge point of all the low-pressure connections 2into the manifold line 3, upstream of the inlet-side end 41 of theelectric fuel pump 6 acting as a forward feed pump. The electric fuelpump 6 pumps fuel out of the fuel tank 35 and via the second fuel supplyline 6.1 to the high-pressure pump 34. The high-pressure pump 34 inturn, via the supply line 32, subjects the high-pressure collectionchamber 31 (common rail) to fuel that is at very high pressure. The fuellevel is in the range between about 1500 and 1600 bar.

In this case, by means of the throttle restriction 7, it is attained athigh load points that because of the pressure prevailing in the systemchamber 10, filling of the hydraulic coupling chamber 14 is establishedvia the leakage gaps between the positive displacement piston 18 and thehousing 44, and between the actuating piston 15 and the housing 44. Atlow load points, the pressure required for filling the coupler can bemaintained by the electric fuel pump 6, serving as a prefeed system. Asa result, downstream of the throttle restriction 7, only the slightpressures of the electric fuel pump now prevail, which can beapproximately between 3 and 8 bar. As a result, a substantial relief ofthe low-pressure side 10 of the fuel injector 10 can be attained. By thechoice of the diameter of the throttle restriction 7 in the manifoldline 3 and of the feed pressure of the electric fuel pump 6, thepressure in the system chamber 20 for filling the hydraulic couplingchamber 14 through its guidance gaps can be varied if needed. If anelectric fuel pump 6 together with a high-pressure pump 34 is used, thenthe electric fuel pump 6 associated with the fuel tank acts as a prefeedsystem for the high-pressure pump 34, which is not embodied asself-aspirating. In this case, the supply line 6.1 branches off from thefuel line assigned to the fuel tank 35 and leads to the high-pressurepump 34.

Various filling pressures for filling the hydraulic coupling chamber 14of the hydraulic booster 13 can be preset to suit a particular need, bymeans of the design of the diameter of the throttle 7 in the manifoldline 3, and the adjustment of the opening pressure of the pressureholding valve 8 and of the feed pressure of the electric fuel pump 6.

By means of the reception, proposed according to the invention, of athrottle restriction 7 in the manifold line 3, both an electric fuelpump 6 and a pressure holding valve 8 can be mechanically relieved interms of their pressure relief at high load points of the engine 36,which results in a substantial relief of the low-pressure system 10 ofthe fuel injector 38. Both the pressure holding valve 8 and the electricfuel pump 6 can therefore be made smaller with respect to theirstrength. In particular, by the provisions proposed according to theinvention, the use of additional mechanical components that have to bemade and moved can be avoided, thus also making it possible to dispensewith adjustment procedures on these inner parts that would additionallyhave to be provided.

LIST OF REFERENCE NUMERALS

-   1 Cylinder-   2 Low-pressure connection-   3 Manifold line-   4 Pressure holding valve-   5 Fuel return-   6 Electric fuel pump-   6.1 First supply line-   7 Throttle-   8 Pressure holding valve-   8.1 Second supply line-   9 High-pressure system of fuel injector-   10 Low-pressure system of fuel injector-   11 Actuator-   12 Piezoelectric crystal stack-   13 Hydraulic booster-   14 Hydraulic coupling chamber-   p_(K) Coupling chamber pressure-   15 Actuating piston-   16 End face of actuating piston-   17 Connection-   18 Adjusting piston-   19 Closing element-   20 System chamber-   21 Closing element seat-   22 Outlet conduit-   23 Guide piston-   24 Control chamber-   25 Control chamber inlet-   26 Spring element-   27 Injection valve member-   29 Face end of injection valve member-   31 High-pressure collection chamber (common rail)-   32 Supply line-   34 High-pressure pump-   35 Fuel tank-   36 Internal combustion engine-   37 Cylinder head region-   38 Fuel injector-   39 Housing-   40 High-pressure connections-   41 Inlet of 6, 8 on the side toward the injectors-   42 Bellows-   43 Wall-   44 Housing coupling chamber

1-10. (canceled)
 11. A fuel injection system for internal combustionengines, comprising a plurality of fuel injectors each having onehigh-pressure connection and one low-pressure connection, thelow-pressure connections each discharging into at least one manifoldline, the fuel injectors being actuatable via a piezoelectric actuator,a means, located between the manifold line and a pressureless fuelreturn, for maintaining fuel pressure in the manifold line, the fuelinjectors each including a system chamber, in which a pressure levelsuitable for filling a hydraulic coupling chamber prevails, and athrottle located between the discharge point of the low-pressureconnections of the fuel injectors into the manifold line and the inlet,on the side toward the injectors, of the means for maintaining the fuelpressure in the manifold line.
 12. The fuel injection system accordingto claim 11, wherein the means for maintaining the fuel pressure isembodied on the low-pressure side as a pressure holding valve.
 13. Thefuel injection system according to claim 11, wherein the means formaintaining the fuel pressure is represented on the low-pressure side byan electric fuel pump.
 14. The fuel injection system according to claim11, wherein the high-pressure connections of the fuel injectors aresubjected to fuel at high pressure from at least one high-pressurecollection chamber.
 15. The fuel injection system according to claim 11,wherein the stroke of the piezoelectric actuator can be transmitted toan injection valve member via a hydraulic medium, in particular fuel, bymeans of a hydraulic coupling chamber of the hydraulic booster, and thehydraulic coupling chamber can be filled with the hydraulic medium viathe at least one throttle.
 16. The fuel injection system according toclaim 11, wherein, at relatively high load ranges of an internalcombustion engine, a coupling chamber pressure p_(K) can be maintainedvia the throttle in the manifold line.
 17. The fuel injection systemaccording to claim 12, wherein the pressure required for filling thehydraulic coupling chamber is maintained, at low load points of theengine, by means of the pressure holding valve.
 18. The fuel injectionsystem according to claim 13, wherein the pressure required for fillingthe hydraulic coupling chamber is maintained, at low load points of theengine, by means of the pressure holding valve.
 19. The fuel injectionsystem according to claim 11, wherein the initial filling of thehydraulic coupling chamber is effected via leakage gaps between anactuating piston and a housing and/or via leakage gaps between anadjusting piston and the housing, the housing being surrounded by thesystem chamber.
 20. The fuel injection system according to claim 13,wherein the electric fuel pump on the low-pressure side of the fuelinjector is located upstream of a high-pressure pump.
 21. The fuelinjection system according to claim 12, wherein the pressure holdingvalve in the manifold line is located upstream of a fuel tank.